Metal ingots, billets and other castparts may be formed by a casting process which utilizes a vertically oriented mold situated above a large casting pit beneath the floor level of the metal casting facility, although this invention may also be utilized in horizontal molds. The lower component of the vertical casting mold is a starting block. When the casting process begins, the starting blocks are in their upward-most position and in the molds. As molten metal is poured into the mold bore or cavity and cooled (typically by water), the starting block is slowly lowered at a pre-determined rate by a hydraulic cylinder or other device. As the starting block is lowered, solidified metal or aluminum emerges from the bottom of the mold and ingots, rounds or billets of various geometries are formed, which may also be referred to herein as castparts.
Around the mold outlet of some of these molds is a permeable perimeter wall, which in the case of circular diameter castparts, is a circular ring. Any one of a number of different shapes may be utilized in the casting mold, with no one in particular being required to practice this invention. While the permeable perimeter wall is typically made from graphite, it may also be made from other material. The permeability of the perimeter wall allows a gas and/or a lubricant to be forced through the wall and provide a gas force around the mold on the castpart being molded. The gas and the lubricant enhance the molding process and the quality of the castpart.
While the invention applies to the casting of metals in general, including without limitation aluminum, brass, lead, zinc, magnesium, copper, steel, etc., the examples given and preferred embodiment disclosed may be directed to aluminum, and therefore the term aluminum or molten metal may be used throughout for consistency even though the invention applies more generally to metals.
While there are numerous ways to achieve and configure a vertical casting arrangement, FIG. 1 illustrates one example. In FIG. 1, the vertical casting of aluminum generally occurs beneath the elevation level of the factory floor in a casting pit. Directly beneath the casting pit floor 101a is a caisson 103, in which the hydraulic cylinder barrel 102 for the hydraulic cylinder is placed.
As shown in FIG. 1, the components of the lower portion of a typical vertical aluminum casting apparatus, shown within a casting pit 101 and a caisson 103, are a hydraulic cylinder barrel 102, a ram 106, a mounting base housing 105, a platen 107 and a starting block base 108 (also referred to as a starting head or bottom block), all shown at elevations below the casting facility floor 104.
The mounting base housing 105 is mounted to the floor 101a of the casting pit 101, below which is the caisson 103. The caisson 103 is defined by its side walls 103b and its floor 103a. 
A typical mold table assembly 110 is also shown in FIG. 1, which can be tilted as shown by hydraulic cylinder 111 pushing mold table tilt arm 110a such that it pivots about point 112 and thereby raises and rotates the main casting frame assembly, as shown in FIG. 1. There, are also mold table carriages which allow the mold table assemblies to be moved to and from the casting position above the casting pit.
FIG. 1 further shows the platen 107 and starting block base 108 partially descended into the casting pit 101 with castpart or billet 113 being partially formed. Ingot 113 is on the starting block base 108, which may include a starting head or bottom block, which usually (but not always) sits on the starting block base 108, all of which is known in the art and need not therefore be shown or described in greater detail. While the term starting block is used for item 108, it should be noted that the terms bottom block and starting head are also used in the industry to refer to item 108, bottom block typically used when an ingot is being cast and starting head when a billet is being cast.
While the starting block base 108 in FIG. 1 only shows one starting block 108 and pedestal 115, there are typically several of each mounted on each starting block base, which simultaneously cast billets, special shapes or ingots as the starting block is lowered during the casting process.
When hydraulic fluid is introduced into the hydraulic cylinder at sufficient pressure, the ram 106, and consequently the starting block 108, are raised to the desired elevation start level for the casting process, which is when the starting blocks are within the mold table assembly 110.
The lowering of the starting block 108 is accomplished by metering the hydraulic fluid from the cylinder at a pre-determined rate, thereby lowering the ram 106 and consequently the starting block at a pre-determined and controlled rate. The mold is controllably cooled during the process to assist in the solidification of the emerging ingots or billets, typically using water cooling means.
There are numerous mold and casting technologies that fit into mold tables, and no one in particular is required to practice the various embodiments of this invention, since they are known by those of ordinary skill in the art.
The upper side of the typical mold table operatively connects to, or interacts with, the metal distribution system. The typical mold table also operatively connects to the molds which it houses.
When metal is cast using a continuous cast vertical mold, the molten metal is cooled in the mold and continuously emerges from the lower end of the mold as the starting block base is lowered. The emerging billet, ingot or other configuration is intended to be sufficiently solidified such that it maintains its desired shape. There is an air gap between the emerging solidified metal and the permeable ring wall. Below that, there is also a mold air cavity between the emerging solidified metal and the lower portion of the mold and related equipment.
After a particular cast is completed, as described above, the mold table is typically tilted upward and away from the top of the casting pit, as shown in FIG. 1. When the mold table is tilted or pivoted, and without a lubricant control system, the lubricant tends to drain out of the conduits and leaks either into the casting pit or on the floor of the casting facility.
The use of a permeable or porous perimeter wall has proven to be an effective and efficient way to distribute lubricant and gas to the inside surface of a continuous casting mold, one example of which is described in U.S. Pat. No. 4,598,763 to Wagstaff, which is hereby incorporated herein by this reference as though fully set forth herein.
In the typical use of a permeable perimeter wall, lubricant and gas are delivered to the perimeter wall under pressure through grooves or delivery conduits around the perimeter wall, typically using one delivery conduit (if grooves are used for the delivery of lubricant) and one or two delivery conduits (grooves) for the delivery of gas. The preferred lubricants are synthetic oils, whereas the current preferred gas is air. The lubricant and gas then permeate through the perimeter wall and are delivered to the interior of the mold as part of the casting process.
The perimeter walls on existing mold tables each have delivery conduits to deliver the lubricant and/or gas, and the delivery conduits may be circumferential groove-shaped delivery conduits with the same depth and width, or they may be holes partially drilled through the perimeter walls, or any other delivery means for that matter. The typical perimeter wall has a separate lubricant delivery conduit and a gas conduit.
Although embodiments and aspects of this invention are directed to graphite rings, applications of this are not limited to graphite. Graphite has proven to be the preferred permeable material for use as the perimeter wall material or media.
It is desired in some embodiments of this invention to have the same mass flow of gas through each permeable ring on a given mold table. In the typical prior art mold the pressure at which gas was supplied to each ring was generally the same pressure, although the pressure was raised and/or lowered to all permeable perimeter walls before, during and after startup.
No two permeable rings are identical and each allows the passage of gas or gas flow a little differently. Furthermore as the life of a particular permeable ring passes, its permeability decreases due to any one of a number of different factors (clogging, varnishing, or simply the characteristics of that individual permeable ring, etc.).
Prior art pressure based systems which force the gas through the permeable rings generally provide the same pressure gas to all the permeable rings. While it is desirable to achieve the same mass flow rate of gas through each permeable ring on a mold table, the practicalities of the differences in each permeable ring and the rate at which their permeability decreases, creates a situation in which the mass flow rate of gas through the different permeable rings differs or varies. This is especially true if the gas flow supplied to all permeable rings on a mold table is the same. Trying then to achieve approximately equal flow generally requires operator adjustment of the pressure at each mold, which requires operators to spend more time at the casting pit than desired.
Since the inlet pressure for the table provides one pressure for the gas flow, if the pressure valve is manually turned up to increase the flow to the permeable rings which are clogging first, then this also has the undesirable affect of increasing the pressure and consequently the flow to the other permeable rings which are allowing more flow through.
In the prior art, typically on or just before the startup of casting on a given mold table, the pressure regulator would be manually set to a particular pressure, such as sixty pounds per square inch for the entire table. On startup the pressure would be turned up for example to one hundred pounds per square inch, and then after the startup phase, the pressure would be turned back down to seventy or eighty pounds per square inch for the run pressure. It has typically been a pressure based operation for achieving gas flow to the individual molds on a mold table which utilize permeable perimeter walls. This generally required personnel in or around the casting pit.
It is an object of some embodiments of this invention to provide a gas flow system which provides a more uniform gas mass flow rate or gas flow rate through the permeable perimeter walls in the molds on a given mold table.
It is also an objective of some embodiments of this invention to provide a gas mass flow control system which controls the flow of gas to each individual mold on a table more closely and in a more automated fashion, thereby requiring less operator presence at or around the casting pit.
Some embodiments or aspects of this invention provide a mass flow meter which can be positioned outside of the casting pit area if desired. Embodiments of this invention key on the measurement the mass flow of the gas, which results in a more consistent mass flow of gas through each permeable ring and a more equal flow rate to each of the plurality of permeable perimeter walls on a given mold table.
It will also be appreciated by those of ordinary skill in the art how this invention's utilization of a Supervisory Control and Data Acquisition (“SCADA”) data logging system which logs critical and non-critical mold operating parameters may be utilized in the overall casting process control and allow for the establishment of set points for one or more of the parameters for better process control and failure prevention. The recording and monitoring of casting gas flows and mold “back-pressure” for instance provides the ability for process improvement and mold condition evaluation. This type of data gathering may be used to provide the operator alarms for any one or more of numerous action items, such as providing an alarm that the mold is ready to be removed from the casting table and replaced.
Other objects, features, and advantages of this invention will appear from the specification, claims, and accompanying drawings which form a part hereof. In carrying out the objects of this invention, it is to be understood that its essential features are susceptible to change in design and structural arrangement, with only one practical, and preferred embodiment being illustrated in the accompanying drawings, as required.